Many different polymer-based compositions have been utilized to form sealing elements for applications such as foodstuff applications both liquid and dry commodities, medical products and nutritional products. Examples of such polymers are polyolefins, polyvinyl halides such as polyvinyl chloride and polyvinylidene chloride, elastomers and, various rubbers such as EPDM, polyesters, polycarbonate. Techniques used to manufacture sealing elements are set forth, for examples, in U.S. Pat. Nos. 3,183,144; 3,300,072; 3,414,938; 3,493,453; 3,779,965; 3,786,954; 4,085,186; 4,619,848; 4,717,034; 4,939,859; 4,981,231; 4,984,703; 5,000,992; 5,104,710; 5,137,164; and 5,215,587 all herein incorporated by reference.
In one embodiment, sealing elements in the form of a single layer or liner are made by extruding a polymer composition, cutting and placing a quantity of the extrudate at a desired location, such as in the center of a cap, followed by compression molding the extrudate into a gasket or liner. In other embodiments, injection molding can be utilized to form a sealing element in the form of a seal ring, for example, in a cap.
Properties required of the sealing elements can vary depending upon individual applications. For example, sealing elements subject to retort conditions, such as relatively high temperatures and pressures, are generally required to withstand the retort process without failing, maintain a suitable oxygen barrier for a desired lifespan of the product and also be easily removable from the container when desired by a consumer or other user. Regardless of whether or not retort conditions are encountered, the sealing element should provide for adequate sealing at a wide range of temperatures, especially high temperatures. Various sealing elements should also provide desirable sealing properties during stacking and a reasonable oxygen barrier property when required to preserve freshness of a packaged item, such as a foodstuff. Some sealing elements must be resistant to acids or bases. Sealing elements whether designed for a single use or a multiple use item should retain their integrity and not shred or tear in order to prevent contamination of the packaged products. Further, seal elements should have good compression set to impart sealing capability and not lose seal integrity. Numerous attempts to provide sealing elements had been disclosed.
U.S. Pat. No. 7,960,007 and U.S. Patent Publication No. 20110204016 relate to retort liners and containers including a container body such as a bottle or jar, a closure, and the retort liner, wherein the retort liners exhibit attractive properties such as low compression set under retort conditions, desirable adhesion to a polymeric closure such as a cap or lid, and beneficial oxygen barrier properties. In particular, the retort liners are thermoplastic elastomers formed from compositions including one or more styrenic block copolymers, one or more polyolefins and a softener. In a preferred embodiment, the retortable containers are all plastic packages, wherein the bottle or jar and the closure are thermoplastic compositions and the liner is a thermoplastic elastomer composition.
U.S. Pat. No. 4,807,772 relates to a polypropylene compression molded closure with an elastomer liner that is removable, the elastomer being a blend of polyethylene and a rubbery copolymer, containing oil.
U.S. Pat. No. 4,872,573 relates to a moldable plastic closure comprising a selectively foamed, unitarily molded layer and at least one layer of barrier resin adapted to retard the migration of oxygen-containing gasses through the closure.
U.S. Pat. No. 5,000,992 relates to a plastic container closure, such as a bottle cap liner or tamper evident seal, formed from a coextruded multilayer foamed film. The coextruded multilayer foamed film has at least one solid film layer of a first polyolefin blend containing linear low density polyethylene, low density polyethylene, and, optionally high density polyethylene, and at least one foamed layer of a second polyolefin blend containing linear low density polyethylene, low density polyethylene, and optionally ethylene vinyl acetate. The multilayer foamed film may be coextruded using a blown film or cast film extrusion process under defined conditions. The coextruded multilayer foamed film may be laminated to other materials such as polyester film, thermoplastic adhesive films or metallic films and used as a plastic container closure, or may be applied as a liner to a plastic bottle cap.
U.S. Pat. No. 3,786,954 relates to a cap liner disclosed for use with a closure cap in sealing a container. The liner is cut from a foamed polyethylene sheet material. It reportedly provides a seal for products such as fine powdered products where leakage has been experienced with prior liners. The foamed liner material reportedly has dynamic cushioning properties so that a tight seal is maintained at all times including handling and shipping operations of the sealed package. One embodiment of the closure is a laminate of the foamed sheet material and a thin air impervious film.
U.S. Pat. No. 5,104,710 relates to a gasket of thermoplastic material moulded in a polypropylene cap, wherein the adhesion of the gasket to the cap at temperatures below 200° C. is reportedly improved by including an adhesion-promoting polymer of propylene in the thermoplastic composition.
U.S. Pat. No. 4,529,740 relates to hot melt compositions disclosed from which foamed products having a fine and uniform void structure therein can be obtained. The compositions include a thermoplastic polymer preferably an elastomer such as a styrene-butadiene block copolymer, and a small amount of a salt of a sulfonated styrene polymer. Plasticizing processing aids, tackifying agents and antioxidants can be included in the compositions, as well as in addition surfactants such as dodecylbenzene sulfonate. The composition can be mixed with gaseous blowing agents by suitable means and dispensed to produce foamed products reportedly suited for example as sealants in closures for containers.
U.S. Pat. No. 4,744,478 relates to a molded polymeric container closure comprising at least one substantially unfoamed polymer layer and an integrally molded foamed layer of the same polymer.
Numerous olefin block copolymers and olefin block copolymer containing compositions are described in U.S. patent and Publication Nos. U.S. Pat. Nos. 7,671,106; 7,608,668; 6,566,446; 6,545,088; 6,538,070; 6,448,341; 5,869,575; 5,844,045; 2010/0298515; 2010/0069574; and 2007/0219334. These disclosures set forth a plethora of various potential applications, end uses, and general components that can be combined therewith.
U.S. Pat. No. 7,671,106 relates to cap liners, closures and gaskets for multi-block polymers, i.e. olefin block copolymers. The polymer composition comprises at least an ethylene/alpha-olefin interpolymer and at least one other polymer. The other polymer can be selected from a second ethylene/alpha-olefin interpolymer, an elastomer, a polyolefin, a polar polymer, and an ethylene/carboxylic acid interpolymer or ionomer thereof. The ethylene/alpha-olefin interpolymer is a block copolymer having at least a hard block and at least a soft block. The soft block comprises a higher amount of comonomers than the hard block. The block interpolymer has a number of unique characteristics disclosed here. Also provided are gaskets, bottle cap liners, and closures that comprise or are obtained from a composition comprising at least one ethylene/alpha-olefin interpolymer and at least one polyolefin. The gaskets are reportedly capable of compression sealing various containers, without contaminating the contents. Liquid containers reportedly particularly benefit from the use of the novel gasket materials disclosed herein.
In view of the above, a problem still exists as economical sealing elements especially polyolefin-based sealing elements, are needed that are formed from compositions providing broad processing windows for depositing a sealing element bead, for example in a closure or cap, and further forming a sealing element, such as a liner, having desirable barrier properties, particularly when using a container and/or closure formed from a substantially homopolymer polyolefin. It is a difficult challenge to meet the processing requirements to make a sealing element, as well as the performance requirements needed when the sealing element is in a packaged state. Additionally, there is a need for sealing elements that are formed from polyolefin compositions that are readily processable under desired conditions that do not contribute to one or more of taste and odor of the packaged product, provide desirable compression set properties to ensure good sealing, provide good adhesion to a polymeric cap or closure, and provide oxygen barrier properties, which are especially useful in foodstuff applications.